1. Field of the Invention
This invention relates in general to an audio signal processing device, a signal recovering device, an audio signal processing method and a signal recovering method.
2. Description of Related Art
Recently, an audio sound that is compounded by a regulation-compounding technique or an editing-compounding technique is widely used. These techniques compound audio sound by connecting the audio sound constructing elements (such as audio sound elements).
Generally speaking, a compound audio sound is used after it is suitably embedded with an attaching information by an electronic watermark technique. In order to discriminate a compound audio sound and a real-person-made-audio sound or in order to identify a speaker who makes an audio sound element serving as a compound audio sound element or a composer who makes the compound audio sound. The attaching information is embedded into the compound audio sound to show the originality and/or the composing right of the compound audio sound.
The electronic watermark is produced by using an effect that approaches frequency with high strength composition and ignores that with small strength with respect to human hearing (a masking effect). More specifically, it is produced by approaching frequency with a high strength composition while deleting a composition that is smaller than this composition and inserting an attaching signal that occupies a band same as the deleted composition in the spectrum of a compound audio sound.
Moreover, the inserted attaching signal is generated in advance by modulating a carrier wave with a frequency around the upper limit of the band occupied by the compound audio sound through using an attaching information.
Regarding the techniques of identifying the speaker who makes an element of a compound audio sound such as an audio sound element and recognizing the originality and/or the composing right of the compound audio sound, a method is provided to encrypt the data that express the audio sound element and to maintain a decryption key only for the speaker or the right of the composer of the compound audio sound.
However, in the above electronic watermark technique, when the compound audio sound that is inserted by an attaching signal is compressed, the content of the attaching signal will be damaged due to compression, and the attaching signal cannot be recovered. Additionally, when the compound audio sound is further sampled, the composition created by a carrier wave for generating an attaching signal will be regarded as a foreign sound that is audible. A compound audio sound is usually used after it has been compressed, so by using the above electronic watermark technique, the attaching signal attached to the compound audio sound usually cannot be properly reproduced.
Regarding a method for encrypting data that express an element of a compound audio sound such as an audio sound element, it is difficult for a person who does not have a decryption key for these data to use these data. Moreover, with this technique, when the quality of the compound audio sound is very high, discrimination cannot be made between a compound audio sound and an audio sound that is made by a real person.